Ultra-high strength steel is currently used in building construction and static automotive structures (e.g. vehicle bodies and frames). The use of ultra-high strength steel generally allows the weights of these structures to be reduced. Additionally, in automotive structures, the ultra-high strength steel enables the absorption of impact energy and minimizes intrusion into occupant seating areas. Although ultra-high strength steel can be made extremely strong, other properties such as formability, weldability, and impact toughness may be negatively affected, resulting in structures which may be more prone to cracking and fracture.
Power transmission components for automotive vehicles, such as clutch assemblies having clutch plates within a clutch housing and clutch hub are well-known. Such clutch housings have a generally cylindrical or cup-shaped body and an open end. The cylindrical or cup-shaped body is formed from a sheet metal blank and has a plurality of spline teeth formed thereon. The clutch plates fit within the clutch housing and engage the spline teeth. The clutch hub can also be a formed sheet metal component and is typically connected to a transmission shaft.
Powertrain components including clutch housings and hubs are commonly made of aluminum or high strength low alloy steel (HSLA) rather than ultra-high strength steel, such as boron steel. Aluminum or HSLA steel is used primarily because of its formability. Specifically, these types of materials are high strength materials which can achieve a specific geometric dimension or shape and have a specific tolerance required. Consequently, aluminum or HSLA may be used in powertrain components including parts of an automatic transmission easily, efficiently, and at a low-cost.
Typically, components such as reaction shells, clutch housings, and hubs made of aluminum or HSLA are formed using one or a combination of cold-forming or stamping processes and thermal heat treatments to obtain the desired shape, performance, and strength characteristics. Additionally, the structures such as the plurality of spline teeth of the clutch housing may be formed easily by using a series of rollers. Similar processes also may be used to form other powertrain components such as planetary carriers used in differentials and various covers used in a vehicle powertrain.
Ultra-high strength steel lacks formability using the conventional cold-forming technologies discussed above. Use of conventional cold-forming technologies with ultra-high strength steel typically does not result in the formation of required geometric dimensions and tolerances. However, there is a desire by manufacturers and suppliers to utilize ultra-high strength steel in forming automotive components such as power transmission components for similar reasons as those discussed above when used in static applications of automotive structures (e.g. reduced component weight and improved absorption of impact energy).
As such, a need exists for components, such as clutch housings and hubs, to be formed from ultra-high strength steel, such as boron steel. Additionally, there is a need for an improved method for forming the same.